Antifogging composition



' Patented Nov. 22, 1949 2,488,026 aurmoocmo coiurosrnon Richard 1..Gilbert, Jr., on Greenwich, Conn., as signor to American CyanamidCompany, New

York, N.

Y., a corporation of Maine .No Drawing. Application July 2, 1948,

Serial No. 681,141

This invention relates to anti-fogging agents for transparent surfacessuch as glass or the transparent resins such as methyl methacrylate usedin the windshields of automobiles, airplanes, etc. and in opticalinstruments. A principal ob- .iect of the invention is the provision ofan antifog'ging agent that is much more permanent than those that havepreviously been used, and which will therefore maintain itseffectiveness for longer periods of time. The invention will bedescribed with particular reference to military uses, but it should beunderstood that the advantages thereof are also important for otherpurposes and can be obtained whenever it is desired to maintain atransparent surface free from fog or condensed moisture under changingconditions or temperature or humidity.

'An anti-fogging material is required at the present time to maintainthe line of sight free from fog on transparent solid surfaces ofairplanes. Thus, for example, during the flight ofa dive bomber from analtitude of about 8,000 feet (temperature about 32 F.) to sea level, thesudden change in temperature and relative humidity of the air results ina condensation of moisture on the windshield and also on the lenses ofthe bombsight, and this seriously interferes with the eflectiveness ofthe attack. The principal loci of fog are on the surfaces of theaviators goggles and on the external and internal surfaces of the lensesin telescopes. An anti-fogging agent must not only function during thedive, but it must also continue to function in flight and after theoptical equipment has been stored on the ground, and the hot, humidatmosphere of the South Pacific and other tropical combat areas causesthis problem to be particularly severe.

A successful anti-fogging agent must be sufficiently hydrophilic to takeup the water droplets that condense as fog and thus retain a clear,transparent film. For this reason, the anti-fogging agent musthavesurface-active properties and must therefore be at least slightlywatersoluble. 0n the other hand. too high a degree of water-solubilityresults in a rapid removal of the eflective anti-fogging agent from thetransparent surface and it must be renewed at frequent intervals. sodiumdi-(2-ethy1 hexyl) sulfosuccinate is the anti-fogging agent that hasbeen most widely used by the aviation forces of the United States,Canada and Great Britain, but I have found that certain other esters ofsulfosuccinlc acid are equally effective as anti-fogging agents and aremuch more permanent in character because they are less water-soluble.

In order to obtain optimum properties in this class of compounds it isnecessary to maintain an extremely close balance between the wettingpower, which determines the ability of the compound to prevent fog, andthe water-insolubility of the compound, which determines its eflectivelife. Too insoluble a compound does not possess suflicientsurface-activity to distribute the water droplets as a clear, continuousfilm, whereas too soluble a compound is rapidly removed by the condensermoisture. The condensate is always colder than the surroundingatmosphere, and is almost always below 25 C., and therefore thesolubilities referred to are those of the anti-fogging composition incold water.

I have now discovered that the diesters of sulfosuccinic acid withalkyl-substituted hydroaromatic alcohols of 11-13 carbon atoms possessthe requisite characteristics of surface-activity and insolubllity incold water to produce a satisfactory anti-fogging agent that is muchmore permanent in character than those previously used. The termhydroaromatic alcohol designates an alcohol containing a saturated6-membered hydrocarbon ring, and'the alcohol-forming hydroxy group maybe attached to one of the ring carbon atoms, as in the cyclohexanols, orto a carbon atom in a side chain, as in the hexahydrobenzyi alcohols.Representative alcohols of this class containing 11-13 carbon atoms are4-amyl and 4-hexyl cyclohexanol and 4-amyl and 4-isohexylhexahydrobenzyl alcohol of the formula (CH3) 20H. (CH2) 3.CBH10.CH2OHThese esters are preferably used in the form of their sodium, potassium,ammonium or other water-soluble salts, it being understood that the termwater-soluble designates only a limited degree of water-solubility inthe compounds.

The above compounds are prepared by esterifying two mols of the alcoholwith one mol of fumaric or maleic acid or maleic anhydride by standardesterification procedures, as by refluxing a slight excess of thealcohol with the acid in I toluene and excess alcohol were removed bydisconvenient method is to impregnate cloth, paper, tillation at reducedpressure. 355 grams of the felt, sponge or other absorbent material withthe ester was sulionated by refluxing with 96 grams esters, as bysoaking in a strong alcohol solution (7% excess) of sodium bisulfite in350 cc. of ethyl and drying. aiter which the absorbent material alcoholand 100 cc. 01 water for 10 hours. After may b ubbed over the glass to apl a mm m filtering the sulionated product and evaporating oi thewetting agent thereto. to dryness there was obtained 8 grams of so- Thepermanency of the compounds of the indium di-(4-amyicyciohexyl)suli'osuccinate in the vention is shown by the following test: a smalliorm oi a brittle white solid which ground easily amount of solution ofthe material to be tested, to a white powder and formed a clear solution10 either in water or in anorganic solvent,isswabbed in hot water. ontoa clean glass slide and allowed to dry. when The sodiumdi-(d-amylliexahydrobenzyl) sulnecessary the iilm is then polisheduntil, it is rosuccinate and sodium di-id-isoheiwlhexahydr completelytransparent. The slide is chilled to benzyl) sulfosuccinate wereprepared by the same about 0 C. and then dropped into a moistatmosprocedure. Thus. the latter compound was made' phere of 35 C. abovehot water contained in a by heating 110 grams (0.5 mole-+10% excess) offlash. A Bureau of Standards 251! test chart is crudei-isohexylhexahydrobenzyl alcohol with viewed through the slide whilethe latter is maingrams of maleic anhydride, 50 cc. of toluene tained inthe warm, saturated atmosphere and and 1 gram of p-toluene sulfonic acidfor about the number of lines per inch legible after 10 sec- 8 hoursfollowed by washing with alkali solution 20 onds is recorded. Ingeneral.the maximum numand water and extracting the product with but her oflines (56 per inch) can be read through an ethanol to separate thediester from impurities emcient anti-fog material.

present in the crude alcohol used. 60 grams of In order to determine thepermanency of thethe ester were sulionated by agitation with-60 cc.material under test the coated slide is dipped into of ethanol and '15cc. of water containing 14 grams 26 distilled water. allowed to drainand dry and again of sodium bisulflte for 10 hours. tested. Sodiumdloctyl sulfosuccinate, when From the foregoing it will be seen that myintested by this method, permitted complete visivention in its broaderaspects consists in the bility before dipping, but the slide became'fogged provision of anti-fogging compositions containing within 5seconds upon a second test when it had as a principal essentialingredient a diester of so first been dippedinwater and dried. Thesodium sulfosuccinic acid with an alkyl-substituted hysalt of thediester of sulfosuccinic acid with 4-isodroaromatic alcohol of 11-13carbon atoms, prefhexyl hexahydrobenzyl alcohol, when used alone, erabiyinthe form of a water-soluble salt thereof retained its originalanti-fogging properties after and in the application of thesecompositions to having been dipped in water once, and themaxitransparent material such as glass. methyl meth-- mum number oflines on the chart were visible for acrylate and the like. These estersmay be used 5 seconds after the slide was dipped in water as such, or inconjunction with solvents, adheand tested for two additional times. Thesodium sives, other wetting agents, and the like. di- (4-amylcyclohexyl) sulfosuccinate retained its As has been stated, thesuifosucoinate esters original anti-fogging properties after having beenof the present invention are sufficiently hydrodipped in water andtested for 3 successive times, philic to function as'highly eflectiveanti-fogging and was therefore even better than the correagents, yet thepresence therein of two alkylspending 4-isohexyl hexahydrobenzyl alcoholsubstituted hydroaromatic radicals of 11-13 carester.

bon atoms reduces their solubility in cold water Aqueous solutionscontaining 2% p of thesame to such an extent that they are not rapidlyrewetting agents together with 1% of gum tragamoved by the condensedmoisture, and therefore canth or casein gave even more permanent films.possess a long eifective life. I have found how- Those containing sodiumdi-(4-amyl cyclohexyl) ever, as another important feature of myinvensulfosuccinate retained their anti-fogging proption, that thepermanency of these compounds is r l er 88 m y a v t l wh le hose stillfurther enhanced by applying them to the Iwith Sodium -1 y1h ahydrobnzyl) 111-' surface to be protected in admixture with smallerfosucclnate withstood ee t cy les but failed quantities of gums andstarches such as gum 0D e ou th. tragacanth, Irish moss, agar-agar,water-soluble This is a mutinuationqmpart Of y p n ins oralkali-solubilized starches such as cornstarch applicfltmn serial489,496, filed June 3,

and potato starch and alkali-solubilized casein which has Since been ed.

such as sodium or ammonium caseinate. Thus, j whauclaim for example, a1-4% aqueous solution of the An anti-fogging mmposition si 8- sodiumsalt of a diester of suifosuccinic acid with sentla'ny of diester ofsulfosuficimfl d i a an alkybsubstituted hydroaromatic alcohol of 6alkyl-substituted hydroaromatic alcohol or 1143 carbon atoms may bedispersed in a 1% carbon atoms together with a smaller quantity ofaqueous solution of casein containing a preservahydmpmuc colloidselected from-the group sisting of water-soluble gums and starches andtive such as sodium pentachlorphenate and suflialkamsolubmzed casein.

cient ammonia to dissolve the casein, or in 1% An anfldoggmg compositionconsisting aqueous solution of gum tmgacanth may sentially of awater-soluble salt of a diester of cmmm a small amwnt glmrm Filmssulfosuccinic acid with an alkyl-substituted hyformed by swabbmg thesedispefsions the droaromaticalcohol of 11-13 carbon atoms toinnertransparent surfaces of an airplane cockpit gether with a smallerquantity of a member of have given excellent results on test dives. thegroup consisting of watepsoluble gums and The compositions of thepresent invention may starches and alkali solubmzed casein be pp 110 theslass, methyl methaoryla 0r 3. An anti-fogging composition consistingesother r n p Surfaces y ny suitable sentially of a diester ofsulfosuccinic acid with an method. Th y may be ap li d as s h r as slualkyl-substltuted hydroaromatic alcohol of 11-13 tions in ethylalcohol, carbon tetrachloride, solcarbon atoms together with a smallerquantity 0! vent naphtha or other organic solvents. One analkali-solubilized casein.

4. An anti-fogging composition consisting essentially of a diester ofsulfosuccinic acid with an alkyl-substituted hydroaromatic alcohol of11-13 carbon atoms together with a smaller quantity of gum tragacanth.

5. An anti-fogging composition'consisting essentially of a water-solublesalt of a diester of sulfosuccinic acid with an alkyl-substitutedhydroaromatic alcohol of 11-13 carbon atoms together with a smallerquantity of gum tragacanth.

6. An anti-fogging composition consisting essentially of a water-solublesalt of a, diester of sulfosuccinic acid with an alkyl-substitutedhydroaromatic alcohol of 11-13 carbon atoms together with a smallerquantit of an alkali-solubilized casein.

7. A method of inhibiting the formation of fog on transparent materialwhich comprises applying thereto a thin film containing a diester ofsulfosuccinic acid with an alkyl-substituted hydroaromatic alcohol of11-13 carbonv atoms.

8. A method of inhibiting the formation of fog on transparent materialwhich comprises applying thereto a thin film containing a diester ofsulfosuccinic acid with an alkyl-substituted hydroaromatic alcohol of11-13 carbon atoms and also containing a smaller quantity of ahydrophilic colloid selected from the group consisting of water-solublegumsand starches and alkali-solubilized casein.

9. A transparent material having applied to a surface thereof atog-inhibiting coating comprising, as the principal eflectiveanti-fogging agent therein, a diester ofsuliosuccinic acid with analkyl-substituted hydroaromatic alcohol of 11-13 carbon atoms.

uble salt of di-(4-isohe'xyl hexahydrobenzyl) sulfosuccinate.

RICHARD L. GILBERT, JR.

REFERENCES CITED The following references are of record in the file ofthis patent: v

UNITED STATES PATENTS Number Name Date 1,369,708 Roberts Feb. 22,19212,292,097 Vollmer Aug. 4, 1942 2,365,297 Schwelzer Dec. 19, 19442,372,171 Bennett Mar. 27, 1945 2,414,015 Carnes Jan. 7, 1947 2,416,254Gilbert Feb. 18, 1947 FOREIGN PATENTS Number Country Date 835,187 FranceSept. 19, 1938 356,046

France Mar. 4, 1940

